Technical Field
The present invention concerns a method of operating a wind power installation as well as a corresponding wind power installation and also a wind park having a plurality of wind power installations.
Description of the Related Art
Methods of operating a wind power installation are generally known and the present application is based in particular on a wind power installation as shown in FIG. 1 having a pod with rotor and rotor blades on a hub, the pod being mounted rotatably on a pylon. In operation of the wind power installation the wind acts on the rotor blades and thereby produces a rotary movement which generates electric energy in the pod by means of a generator. In particular, the basic starting point adopted here is wind power installations having rotor blades with an adjustable rotor blade angle, so-called pitch-regulated wind power installations.
At wind power installation erection locations at which temperatures around freezing point can also occur there is the danger that the wind power installation and in particular the rotor blades ice up. Thus, in certain weather conditions rotor blades of wind power installations can suffer from the formation of ice, hoarfrost or snow deposits. Necessary conditions are generally a high level of air humidity or rain or snow fall at temperatures just below freezing point. In that respect the most frequent icing temperatures are in the range of −1° C. to −4° C. Usually icing does not occur above +1° C. and below −7° C. At lower temperatures the available air humidity in the air is too slight.
While ice and hoarfrost deposits can reach severities from which there can be a danger to people and objects upon being thrown off, loose snow deposits, which when snow falls, are deposited on generally insignificant regions of the rotor blade, like for example the flange, normally do not represent a danger.
A problem with wind power installations is in particular the danger due to ice falling or being thrown off. In operation of a wind power installation with iced rotor blades, pieces of ice being flung off can result in danger to those in close proximity. When a wind power installation is stopped the danger due to snow and pieces of ice being detached from the wind power installation does not differ substantially from the danger involved with other high structures.
A method of operating a wind power installation having regard to the possibility of icing is described in German laid-open specification DE 103 23 785 A1. Therein operating parameters such as for example the power of the wind power installation in dependence on a boundary condition such as wind speed are basically compared to reference values which occur at the respective wind speed. From deviations between the detected operating parameter and the reference operating parameter it is possible to infer ice accretion and suitable protective measure can be initiated, in particular that includes stoppage of the wind power installation.
That procedure is based on the realization that ice accretion at the rotor blades influences the aerodynamics of the blades and thus the rotor, thereby giving deviations in the performance of the installation. They are recognized and evaluated by the described comparison of the operating parameters.
A problem in that respect is that this kind of detection presupposes a mode of operation of the wind power installation, which is as steady as possible, stable and as uniform as possible.
However such ideal conditions frequently do not prevail in the case of light wind which is assumed approximately at wind speeds below 3 or 4 m/s. In the case of strong wind which is mostly assumed at wind speeds from 20 m/s or 25 m/s the sensitivity of such known methods is often inadequate. Accordingly, any ice accretion evaluations are not very reliable or accurate ones are even impossible.
A similar problem arises if the wind power installation has come to a stop because, in the stopped condition, no operating parameters can be meaningfully compared to predetermined operating parameters. In that case the wind power installation may have come to a stop for entirely different reasons. They include a stoppage because of excessively light wind, stoppage because of excessively strong wind, stoppage for maintenance purposes and also stoppage due to network failure of the connected electric power supply network into which the wind power installation feeds and from which the wind power installation draws energy for maintaining its operational management. Moreover, stoppage of the wind power installation because of a detected ice accretion is also considered.